This is an attractive nuisance, especially when coming from attrs. Make it an error, since it's using field() with no annotation:

@dataclass
class C:
    x = field()

I'm not sure this is worth preventing. I can certainly make it an error, but since dataclasses ignores anything without a type annotation, I don't think it's a big deal. Basically I'd have to look through all class attributes that are of type Field but aren't in the class's __annotations__.

I cannot find the original conversation that caused me to open this issue. If anyone feels strongly that this case should be an error, let me know.

Fine to close as wontfix.

Some part of the discussion is in https://bugs.python.org/issue32428

I still think it is important to flag things like this as an error:

@dataclass
class C:
    x = field()

This is a big bug magnet. Especially taking into account that attrs behave in the opposite way in this case.

But surely when you instantiate this: 
c = C(1)

you'll notice that's an error?

> you'll notice that's an error?

Yes, but there are other scenarios, like using `init=False` or updating existing class definition and forgetting to update call sites (which will still work), etc.

What would we lose by not flagging this as an error? I think there are no legitimate use cases for such code, and implementation is straightforward. If you don't have time I can do this myself.

Thanks for the offer. I've already got the code written, I just need to write some tests. I'll get it done real soon now.

New changeset 56970b8ce9d23269d20a76f13c80e670c856ba7f by Eric V. Smith in branch 'master':
bpo-32505: dataclasses: raise TypeError if a member variable is of type Field, but doesn't have a type annotation. (GH-6192)
https://github.com/python/cpython/commit/56970b8ce9d23269d20a76f13c80e670c856ba7f

New changeset 3b4c6b16c597aa2356f5658dd67da7dcd4434038 by Miss Islington (bot) in branch '3.7':
bpo-32505: dataclasses: raise TypeError if a member variable is of type Field, but doesn't have a type annotation. (GH-6192)
https://github.com/python/cpython/commit/3b4c6b16c597aa2356f5658dd67da7dcd4434038